Vehicles include an internal combustion engine that generates drive torque. More specifically, the engine draws in air and mixes the air with fuel to form a combustion mixture. The combustion mixture is compressed within cylinders and is combusted to drive pistons. The pistons rotatably drive a crankshaft that transfers drive torque to a transmission and wheels. When the engine misfires, the combustion mixture of a cylinder may not combust at all or only partially, and may cause engine vibration and driveline oscillation. A random misfire typically occurs on different cylinders regardless of whether or not they come from consecutive engine cycles.
When a misfire occurs, the speed of the piston can be affected, thereby decreasing and/or increasing engine speed. Rough roads can also cause changes in engine speed that are similar in magnitude to those generated by engine misfire events. Therefore, rough roads may cause engine misfire detection systems to incorrectly detect engine misfire events.
Central limit theory provides that random behavior and/or disturbances typically follow a normal distribution. More specifically, a randomly sampled average of a data set is normal, even if the distribution it is extrapolated from is not. Random engine misfires and/or disturbances caused by rough road scenarios typically follow a normal distribution, but are capable of being distinguished.